Abstract: A control system for a torque converter includes a lock-up clutch provided in a torque converter for connecting an input member and an output member of the torque converter directly. An engaging and disengaging hydraulic device controls an engaging and disengaging action of the lock-up clutch. A shift valve provided with a first and second spools in series controls introduction of a driving hydraulic pressure into the hydraulic device. The first spool of the shift valve is subjected to a first hydraulic pressure at one end, while the second spool is subjected to a second hydraulic pressure at the other end. The first and second spools are subjected to a third hydraulic pressure therebetween.

Abstract: An automatic transmission of a vehicle has a transmission gear mechanism having at least a lower gear-speed and a higher gear-speed, and first and second friction coupling members which are applied or released by hydraulic pressures applied thereto. The first friction coupling member is kept applied when the transmission is in the lower gear-speed and the second friction coupling member is kept applied when the transmission is in the higher gear-speed. A control system for the automatic transmission has a hydraulic control circuit which controls the hydraulic pressure applied to the respective friction coupling members, thereby changing the condition of application of the friction coupling members and causing the automatic transmission to shift, and a control unit which controls the hydraulic control circuit according to the running condition of the vehicle.

Abstract: The multistage transmission gear mechanism is provided with a first and second coupling means for shifting speed stages, each being of a type operable hydraulically and adapted to allow four speed stages from first to fourth speed stages to be selected in accordance with a combination between a coupled state and an uncoupled state of the first and second coupling means. A third coupling means is further provided for ensuring engine braking.The second coupling means is engaged or coupled by a first pilot pressure generated by a first solenoid at the second, third and fourth speed stages. The first coupling means is coupled by a second pilot pressure generated by a second solenoid at the third and fourth speed stages. The third coupling means is coupled at the second and third speed stages.A third solenoid is provided for generating a third pilot pressure which prevails over the first pilot pressure and controls shifting the second coupling means at the third speed stage.

Abstract: In an automatic transmission, a second brake is engaged when the transmission is in second and is released when the transmission is in third and first. The second brake is controlled by a hydraulic actuator. Application of the hydraulic pressure to the hydraulic actuator of the second brake is limited upon upshift from first to second so that the hydraulic pressure is gently applied to the hydraulic actuator. The limitation of application of the hydraulic pressure is nullified upon downshift from third to second.

Abstract: A vehicle automatic transmission including a torque converter, a multiple stage transmission gear mechanism connected with the torque converter and a hydraulic control circuit for automatically selecting one of gear stages of the transmission gear mechanism. The hydraulic control circuit includes a kick-down control device which functions to shift down the gear mechanism when the engine control foot pedal is substantially fully depressed. Depending on the vehicle running condition, the kick-down control device may shift down the gear mechanism by two gear stages. The hydraulic circuit includes control hydraulic circuit which functions to shift down the gear mechanism at first by one gear stage and then by a further one stage. For the purpose, relay valves are provided in kick-down control lines to lower stage shift valves.